Back spotfacer

ABSTRACT

A back spotfacer comprised of a cutting arm mounted in a slotted post on one end of a driving bar so as to be swingable between an inoperative position along the axis of the driving bar and an operative position in the radial direction thereof. A rod slidably extending through the driving bar may be operatively connected with the cutting arm by a rack-and-pinion mechanism to turn the latter between its inoperative and operative positions. A holder having a shank to be inserted in the machine spindle supports the backward end of the driving bar for rotation therewith, in such a manner that when the holder is pressed toward the driving bar, only the rod will be thrusted forwardly to turn and retain the cutting arm in its operative position.

United States Patent [191 Ishiguro et a1.

BACK SPOTFACER Apr. 23, 1974 7/ 1 946 Belanger 408/159 FOREIGN PATENTS OR APPLICATIONS 931,024 7/1955 Germany 408/159 Primary Examiner--Francis S. Husar Attorney, Agent, or Firm-Weiner, Basile & Weintraub [57] ABSTRACT the machine spindle supports the backward end of the driving bar for rotation therewith, in such a manner that when the holder is pressed toward the driving bar, only the rod will be thrusted forwardly to turn and retain the cutting arm in its operativeposition.

8 Claims, 10 Drawing Figures [75] Inventors: Fukutaro Ishiguro; Yoshihiro Tamura; Masao Ootani; Tadashi Yoshida; Hitoshi Abe, all of Utsunomiya, Japan [73] Assignee: Kyoritsii Seiki Corporation,

Utsunomiya-shi, Japan [22] Filed: Feb. 7, 1972 [21] Appl. No.: 224,135

[30] Foreign Application Priority Data Feb. 15, 1971 Japan 46-6130 June 26, 1971 Japan 46-46583 Aug. 12, 1971 Japan 46-61274 Sept. 21, 1971 Japan 46-86140 Sept. 21, 1971 Japan 46-86l39 52] 'U.S. c1. 40s/1s9, 408/l87 [51] Int. Cl 1323b 29/18, 1?.23q 3/00 [58] Field of Search...... 408/159, 180, 187

[56] References Cited UNITEDSTATES PATENTS 963,596 7/1910 Lescure 408/159 4 K56 Nod r2 9 2 u s .7 71 J\\ 1 N N Km \x is BACK SPOTFACER This invention relates generally to spotfacers, and in particular to a novel and improved back spotfacer for use in facing a spot around the inner end of a hole extending through some part of a workpiece such that the spot cannot be faced by the usual spotfacing tools.

BACKGROUND OF THE INVENTION A back spotfacer of prior design usually includes a driving bar and a removable spotfacing cutter. The driving bar is inserted into a hole from its outer end and is advanced therethrough far enough to receive the spotfacing cutter on the projecting end. The driving bar is then rotated and moved back into the hole, until the revolving cutter removes enough material to provide usually a flat surface around the inner end of the hole. However, when a tapered seat must be formed, for example, the spotfacing cutter must be replaced with one designed exclusively for that purpose.

The mechanisms heretofore available for moving the driving bar bac kwardly, while imparting thereto a sufficient torque for spotfacing operation, have also been subject to various disadvantages such as, for instance, mechanical complexity and considerable waste of energy. Ingan attempt to overcome these disadvantages, there has been proposed a back spotfacer comprising a facing cutter swingably mounted on the end of a driving bar through a rack-and-pinion mechanism. The fac-' ing cutter is inserted into a hole together with the driving bar and, with the progress of back spotfacing operation, gradually stands in the radial direction of the driving bar. This prior back spotfacer has its own drawbacks, however, in that highly complicated mechanisms are required for the operative interconnection of the cutter and the driving bar, and that it is incapable of facing a spot with a diameter more than twice the diameter of the driving bar.

. SUMMARY OF THE INVENTION inoperative position along the axisof the driving bar andan operative position inthe radial direction of the driving ;bar. The cutting arm is provided with a cutting The invention provides a back spotfacer which is separable between a front attachment and a holder portion, so that spots of different diameter can be faced by replacement of the front attachment only.

The invention also provides a back spotfacer including safety means against an undue working stress or the like applied to the cutting arm, whereby the cutting arm, holder and other parts of the back spotfacer are protected from damage that may otherwise be caused by such trouble.

The invention provides a back spotfacer wherein the driving bar having the cutting arm is readily separable from the holder portion for maintenance and other purposes. 1

The invention also provides a back spotfacer wherein the angle of the cutting arm in its operative position relative to the driving bar is easily adjustable.

The invention provides a back spotfacer which is capable of facing a spot with a diameter more than twice the diameter of its holder portion.

. BRIEF DESCRIPTION OF DRAWINGS.

FIG. 1 is a schematic axial sectional view explanatory of the fundamental structureof the back spotfacer of this invention. i v

FIG. 2 is an axial sectional view of aback spotfacer constructed in accordance with the concepts of this invention. v

FIG. 3 is a cross sectional view showing a cutting arm and related parts in the back spotfacer of FIG. 2.

FIG. 4 is an axial sectional view of another embodiment of this invention.

FIG. 5 is a cross sectional view taken along the plane of line V-V in FIG. 4.

bit. A rod extends through the driving bar so as to be axially slidable therethrough in order to turn the cutting arm between the inoperative and operative positions thereof. The. spotfacer also includes a holder having a shank whereby the holder is rotated with the driving bar. The rod is moved axially of the driving bar by the holder.

The present invention provides a novel and improved back spotfacer free from the above-mentioned disadvantages of the prior art. I The invention also provides a back spotfacer wherein a cutting arm is mounted on' the end of a driving bar so as to be swingable between inoperative and operative positions, so that the cutting arm in its inoperative position can be inserted into a hole of a workpiece together with the driving bar. The cutting arm is then automatically swung to its operative position with the start of the back spotfacing operation.

FIG. 6 is a cross sectional view taken along the plane of line VI-VI in FIG. 4.

FIG. 7 is a fragmentary longitudinal sectional view taken along the plane of line VII-VII in FIG. 6.

FIG. 8 is an axial sectional view of still another embodiment of this invention.

FIG. 9 is an axial sectional view mentof this invention.

FlGQlO is a cross sectional plane of line x-x in no. 9.

i DETAILED DESCIQIPTION view taken along the Referring now to FIG. 1 todescribe the fundamental structure of a back, spotfacer according to this invention, a driving bar 1' is fixedly provided with a slotted post 2 on its front end. A shaft or pin 3 extending trans versely of the slotted post 2 swingably supports a cutting arm 4 thereon. A rod 8 extending axially through the driving bar 1 abuts on the bottom portion of the cutting arm 4. In this manner, the leftward movement, as viewed in FIG. 1, of this rod 8 will cause the cutting arm 4 to turn to its operative position, where the cutting arm is revolved with the driving bar 1 to spotface the inner surface of the workpiece a. The cutting arm 4 and the rod 8 may be operatively interconnected in various ways, as described later in relation with several embodiments of this invention illustrated in FIGSPZ 7 through 10.

It is necessary that the driving bar 1 and so forth be kept axially immovable during back spotfacing operation, while only the rod 8 is thrusted forwardly relative tothe driving bar 1 by a holder portion of the back spotfacer. Accordingly, although both the driving bar of a further embodi- 1 and the rod 8 are supported by the holder portion so movable relative to the rod 8, as hereinafter made apparent.

In an embodiment of this invention illustrated in FIGS. 2 and 3, the cutting arm 4 swingably mounted on the shaft or pin 3 is formed with pinion teeth 5 on the periphery of its semicircular end, and is fixedly provided with a cutting bit 6. As best shown in FIG. 3, a tapered or inwardly widened guide groove 7 is formed axially of the driving bar 1 to receive the rod 8 of substantially trapezoidal cross-sectional shape. This rod 8 is formed with rack teeth 9 which are in mesh with the pinion teeth 5 on the end of the cutting arm 4.

The above mentioned driving bar 1, cutting arm 4, cutting bit 6, and rod 8 constitute, in combination, an operative component of the back spotfacer in accordance with the present invention. For use this operative component is inserted into a hole of the workpiece a from its outer end, as illustrated in FIG. 2, until any further advancement thereof is checked in a manner noted below. The rod 8 is then urged forwardly, while the entire spotfacer unit is set in rotation. By the clockwise rotation, as viewed in FIG. 2, of the pinion teeth 5 caused by the forward thrust of the rack teeth 9 on the rod 8, the cutting arm 4 is turned in the radially outward direction of the slotted post 2. By the revolution of this radially projecting cutting arm 4, its cutting bit 6 faces a spot b around the inner end of the hole.

In order to ensure positive engagement between the pinion teeth 5 on the cutting arm 4 and the rack teeth 9 on the rod 8, and to regulate the position of the cutting arm 4 according to the shape of a spot to be faced, a'stop 10 is provided which is held within a cylindrical bore 11 extending axially of the driving bar 1 and which 4 has one of its ends projecting forwardly for contact with the cutting arm 4. This stop 10 carries a flange 12 in slidable contact with the inner surface of the bore 11, and a coil spring 13 surrounding the stop 10 is provided on the back of the flange 12 to resiliently urge the stop 10 against the cutting arm 4. A regulating screw 14 is screw-threadedly insertedinto the bore 1 l to support the, rear end of the coil spring 13. This regulating screw 14 is axially. adjustable by being turned with a suitable tool inserted into its hole 15 which is preferably of hexagonal shape. In this manner, when the cutting arm 4 is turned radially outwardly to retract the stop 10 against the expansive force of the coil spring 13, as illustrated in FIG. 2, the regulating screw 14 determines a limit of retraction of the stop l0'and therefore, that of the turn of the cutting arm 4.

The driving bar 1 also includes a cylindrical sleeve 16 formed substantially integral therewith. This sleeve 16 is formed with an integral flange 17 on the periphery of its front end, and with a keyway 18 extending axially on its inner surface. The aforesaid guide groove 7 is in direct communication with the interior of the sleeve 16. On the front side of the flange 17, a flanged cylinder 20 having a retaining ring 21 is provided through a bearing 19 which is preferably of roller type, the flanged cylinder 20 being adapted for abutment on the outer surface of the workpiece a during back spotfacing operation.

A coil spring 22 having one of its ends in contact with the flange 17 is provided on the sleeve 16 of the driving bar 1. A plunger 23 is slidably mounted within the sleeve 16. This plunger 23 projects through the rear end of the sleeve 16. A key 24 is formed on the periphery of the plunger 23 to be received in the aforesaid keyway 18 formed on the inner surface of the sleeve 16, thereby only permitting axial sliding movement of while the forward wider portion thereof slidably receives the sleeve 16 of the driving bar 1. The aforesaid coil spring 22 on the sleeve 16 is thus to be compressed between the flange 17 and the front end of the sleeve 28 of the holder 26. Ordinarily, therefore, the holder 26 together with the plunger 23 and the rod 8 is urged backwardly relative to the driving bar 1 by the coil spring 22, so that the cutting arm 4 normally extends axially of the slotted post 2.

In this condition the back spotfacer is inserted into the hole of the'workpiece a until the flanged cylinder 20 abuts on the outer surface of the workpiece a, while the cutting arm 4 projects out of the inner end of the hole. The shank 25, which may be suitably inserted in the machine spindle (not shown), is now rotated and pressed forwardly. The torque or turning force of this shank 25 is transmitted, on the one hand, through the a holder 26, the pin 27, the plunger 23 and the rod 8, and on the other hand, through the holder 26, the pin 27, the-plunger 23, the sleeve 16 and the driving bar 1. The cutting arm 4 with its cutting bit 6 is thus rotated in the same direction as the shank 25, as indicated bythe arrow in FIG. 2.

The forward pressure exerted at the shank 25 is also conveyed through the plunger 23 to the rod 8. Due to the engagement of the rack teeth 9 on the rod 8 and the pinion teeth 5 on the cutting arm 4, the cutting arm 4 is turned clockwise, as viewed in FIG. 2, to its illustrated position. Theseat b is thus spotfaced around the inner end of the hole by the revolving cutting bit 6.

In spite of the rotation of the driving bar 1, cutting arm 4 and so forth, the flanged cylinder 20-is urged stationarily against the outer surface of the workpiece a because it is maintained independent of the driving bar 1 by the bearing 19. The coil spring 13 resiliently presses the cutting arm 4 forwardly through the stop 10, thereby eliminating the possible effects of the backlash between the pinion teeth 5 and the rack teeth 9. The position of the cutting arm 4 in operation may also be regulated by varying the axial position of the regulating screw 14, as previously mentioned.

Another embodiment of the invention illustrated in FIGS. 4, 5, 6 and 7 may be considered as an improvement of the embodiment of FIGS. 2 and 3, incorporating some novel features hereinafter made apparent. In FIGS. 4, 5, 6 and 7, parts similar to those shown in FIGS. 2 and 3 are designated by like reference characters. No further explanation will be given on such parts. The holder 26 is formed with 'a stepped bore 29 extending eccentrically from its forward (left end as viewed in FIG. 4) end along the axis thereof. A thrust rod 30 is inserted into the backward narrower portion of the bore 29, the thrust rod 30 having a length equal to the length of the narrower portion of the bore 29. A pin 31 extending laterally through the center of the holder 26 is provided across the forward wider portion of the bore 29.

A flange 32 is formed on the periphery of the backwa'rd' end of the holder 26 to support one end of a cylindrical spring cover 34 having a rib 33 in contact with the forward end of the flange 32. The spring cover 34 has a regulating ring 34a and a lock nut 34b screw-threadedly mounted thereon. The coil spring 22, referred to in connection with FIG. 2, is housed within the spring cover 34, with one of its ends supported by the rib 33. The sleeve 16 of the driving bar 1, which slidably receives the holder 26, is formed with a step 35 having a stop ring 36 and with another step 37 supporting the forward end of the coil spring 22. The aforesaid spring cover 34 is slidable on the peripheral part of the sleeve 16 defined by the two steps 35 and 37.

As best shown in FIG. 5, the slotted post 2 on the front end of the driving bar 1 is formed with a semicircular guide groove 7, instead of the tapered guide groove in the preceding embodiment of FIGS. 2 and 3, within which is slidably received the rod 8 of corresponding cross sectional shape. This rod 8 is slidably mounted within the bore la extending longitudinally of the driving bar 1 and is flanged at 39. The bore 1a is stepped at 38 to accommodate a coil spring 41 between the step 38 and the flange 39, the coil spring 41 resiliently urging the rod 8 backwardly.

FIG. 7 best illustrates a slot 40 formed on the rear end of the rod 8 in the direction at right angles with the plane of the rack-teeth 9; As the rod 8 is urged into the bore 29 of the holder 26 by the coil spring 41, the pin 31 is received in the slot 40, while the backward end of the rod 8 comes into contact with the forward end of the thrust rod 30, as may be seen from FIGS. 4, 6 and 7.

The driving bar 1 is additionally formed witha step 42 to support the cylinder 20 which is axially adjustable by means of a regulating nut 43. Bearing means 19 im terposed between the step 42 and the cylinder 20 in this embodiment of the invention includes both a radial bearing which may be of roller type, and a thrust bearing which may be of ball type. The cylinder 20 is prevented from forward movement relative to the driving bar 1 by a snap ring 44, while the regulating nut 43 is provided with a lock bolt 45 thereby to be retained in a'desiredposition on the drivingbar 1. Thus, the degree of insertion of the cutting arm 4 is regulatable accord ing to the depth of the hole of the workpiece a by varying the axial position of the regulating nut 43 relative to the cylinder 20.

A plunger 46, including a smaller diameter portion around which is provided the coil spring 13, is slidably mounted within the cylindrical bore 11 of the driving bar 1 to press against the backward end of the stop 10. The backward end of the plunger 46 is tapered into the shape of a cone for contact with the similarly tapered leading end of the regulating screw 14 inserted into a tapped hole 11; extending between the bore 11 and the peripheral surface of the driving bar 1. By the radial movement of the regulating screw 14, the axial position of the plunger 46 within the bore 1 l is variable to regulate the angle of the cutting arm 4. The coil spring 13 serves to eliminate the effects of the backlash between the intermeshing pinion teeth5 and rack teeth 9.

The sleeve 16 of the driving bar 1 is associated with the holder 26by means illustrated inFIGS. 6 and 7 in particular. In diametrically opposite positions on the periphery of the holder 26, there are formed a keyway 47 anda groove 48, the groove 48 including a curved bottom portion 49 where it gradually diminishes in depth toward the forward end of the holder 26. A key 50 extending radially through the sleeve is received in the groove 48. The resiliently yieldable projection 51 includes an outer sleeve 51a telescopically receiving an inner sleeve 51b in which is housed a coil spring 510, the inner sleeve 51b being resiliently urged outwardly by the coil spring 51c against the bottom surface 52 of the groove 48.

As may be apparent from the foregoing description, the holder 26 and the driving bar 1 in this embodiment of the invention are separable from each other. It is impossible that the cutting arm 4 might be prevented from returning to its. inoperative position within the slotted post .2 due to the particles of removed metal which have accumulated between the pinion teeth 5 and the rack teeth 9; then, the back spotfacer unit cannot be detached out of the hole. The holder 26 and the associated parts may then be pulled backwardly, so that, partly owing to the force of the coil spring 22 interposed between the holder 25 and the sleeve16 of the driving bar 1, the key 50 and the resiliently yieldable projection 51 are moved forwardly of the keyway 47 and the groove 48, respectively, relative to lthChOldfil' 26. As the resiliently yieldable projectionSl engagesthe curved bottom portion 49 of the groove 48, the holder 26 is temporarily prevented from moving out of the sleeve 16. r

F urther backward pressure exerted on the holder 26,

however, will cause the resiliently yieldable projection 51 to be contacted by the curved bottom portion 49 and to move forwardly relative to the holder 26 while in sliding-contact with the curved bottom portion 49.

As the holder 26 and the associated parts are removed.

in this manner, the driving bar 1 and so forth are left within the hole. The cutting arm 4 and the backward end of the rod 8 may then be manually moved, and the metal particles suitably removed from between the pinion teeth 5 and the rack teeth 9, to return the cutting arm 4 to its inoperative position within the slotted post 2.

Illustrated in FIG. 8. is a further embodiment of the invention designed particularly for universal use. Only the novel features incorporated in this embodiment are described in the following, parts similar to those shown in the preceding drawings being indicated by like reference characters. A pinhole 53 extends through the flange 32 on the backward end of the holder 26, the pinhole 53 crossing the narrower portion of the bore 29 which extends into the shank 25. A safety pin 54 having two smaller diameter portions in the mid-part thereof is inserted into the pinhole 53 in such a manner that the smaller diameter portions are positioned in the bore 29. This safety pin 54 must be such that upon :application of a predetermined lateral pressure to the mid-part thereof, the pin 54 is broken or severed at its two smaller diameter portions.

The thrust rod 30 mounted within the bore .29 includes a forward large diameter portion and a backward small diameter portion. A coil spring 55 is mounted between the step of this thrust rod 30 andthe step of the bore 29. By means of a key received ina -keyway57, the thrust rod 30 is retained so as to be nonrotatable and immovable in the forward direction. The

backward end of the thrust rod 30 is pivoted on the mid-part of the aforesaid safety pin 54.

The driving bar 1 in this embodiment of the invention is broadly comprised of the sleeve 16 and a detachable front attachment 58 described later in greater detail. Three eccentric bores 59 extend through the sleeve 16 between its rear end and the flange 17. A coil spring 22 is mounted within each of the bores 59, each coil spring 22 being supported between the bottom 60 of the bore 59 and the rib 33 of the spring cover 34,

attachment comprising the driving bar 1, the slotted.

post 2, the cutting arm 4 having the pinion teeth 5, the rod. 8 having thefrack teeth 9 and being resiliently urged. backwardly by the coil spring 41 exercising its expansive force against the flange 39, and the stop 10."

The driving bar 1 in this embodiment of the invention is formed with .a step 65 and a beveled edge 64b. A pin 66 projects into the beveled edge 64b. A nut 67 having a rib in contact with the step 65 and an abutment 68 are mounted on the driving bar 1. The abutment 68 includes a step 69 and a sleeve portion 70 to be fitted into the regulating nut 43. A circular groove 71 is formed on the periphery of the sleeve portion 70.

The front attachment 58 of the above described construction must be inserted into the sleeve 16 while the bolt 61 is fully retracted into the regulating nut 43, in such a manner that the bevelededge 64b of the driving bar 1 rests on the beveled edge 64a of the sleeve 16.

The pin 66 is received in the slot 62 of the sleeve 16.

The nut 67 is fully turned on the screw thread 63. The front attachment 58 is thus mounted on the front end of the sleeve 16. The rod 8 is now in end-to-end abutment on the thrust rod 30. The abutment 68 is mounted on the driving bar 1 in such a manner, that its sleeve portion 70 is fitted into the regulating nut 43. The bolt 61 is'then fully screwed into the regulating nut 43, with the result that its leading end is received in the circular groove 71 on the periphery of the sleeve portion 70 of the abutment 68. In this manner the abutment 68 is free to rotate on the driving bar 1 while being axially immovably retained by the regulating nut 43.

Since the front attachment 58 is readily replacable with similarly constructed attachments having various cutting bits 6 on their arms 4, various sizes of spots b can be faced by this embodiment of the invention. Moreover, in case an excessive working stress has been applied to the cutting arm 4 during a back spot-facing operation, thereby preventing the advancement of the rod 8, the.undesired advancement of only the holder 26 results in the severance of the safety pin 54 at its two smaller diameter portions as the thrust rod 30 presses against the mid-part of the safety pin 54. The undue pressure exerted by the holder 26 in the forward direction is thus substantially absorbed, thereby preventing damage which may otherwise be suffered by the cutting arm 4.

A'further embodiment of the invention illustrated in FIGS. 9 and 10 may be used for spotfacing a deeper seat b, or a counterbore, around the'inner end of a hole extending through a workpiece a. The depth of a seat b or the like faced by the back spotfacers disclosed hereinbefore is determined by the position of the radially projecting cutting arm 4. For spotfacing a deeper seat b or the like, therefore, the cutting arm 4 in its radially projecting operative position must be both revolved and moved toward the outer end of the hole. To this end, the coil spring 55 in this embodiment is mounted within the bore 29 which extends almost fully into the shank 25. A thrust rod 30 having a flange 72 on its forward end is inserted into the forward portion of the coil spring 55, and is resiliently urged forwardly by this coil spring which abuts on the flange 72.

The sleeve 28 of the holder 26 in this embodiment is formed with an axially elongatedguide slot 73 and is provided with a pin 74 projecting into the interior of the sleeve 28 for engagement with the rod 8. A cylindrical ball bearing 75 also having an elongated guide slot in agreement with that of the sleeve 28 is mounted within the sleeve 28, and a differential gear means interconnecting the driving bar 1 and the rod 8 as hereinafter described in greater detail is mounted further within the-cylindrical ball bearing 75. While the driving bar 1 and the rod 8 may be combined as in any of the preceding embodiments of this invention, the intermediate portion of the former and the backward portion of the latter are recessed so as to form a certain spacing therebetween. Rack teeth 76 and 77 are formed opposingly on the recessed surfaces of the driving bar 1 and the rod 8, respectively. The aforesaid pin 74 retains the rod 8 so as to be axially immovable relative to the sleeve 28 of the holder 26. The driving bar 1 is resiliently urged forwardly by the flange 72 on the thrust rod 30. The driving bar 1 and the rod 8 include spacer portions 78 and 79, respectively.

The cutting arm 4 in this embodiment of the invention is constructed differently from those of the preceding embodiments. The cutting arm 4 is formed with a support 4a having a roller 4b and is provided with a cutting bit 6 as illustrated in FIG. 9. A flat spring 80 secured on the forward end of the driving bar 1 resiliently urges the cutting arm 4 forwardly.

The rod 8 is formed with a recessed surface 81 for supporting the cutting arm 4, a projection 82 for returning the cutting arm 4 to its illustrated inoperative position, a transverse groove 83 for receiving the roller 4b of the cutting arm support 4a, and a surface 84 for turning the cutting arm 4 to its operative position.

The cylinder 20 on the sleeve 28 is provided with the regulating nut 43 which directly abuts on the outer surface of the workpiece a. In this embodiment the regulating nut 43 isscrew-threadedly mounted on a bearing holder 86 retained in position by a ring 85. Other details of construction and operation regarding the cylinder 20 are substantially as already set forth in relation with the precedingly disclosed embodiments of this invention.

FIG. 10 best illustrates an elongated guide slot 87 extending axially through the cylinder 20 in agreement with the aforesaid guide slot 73 formed in the sleeve 28 and the cylindrical ball bearing 75, to accommodate a shaft 89 therewithin. An axially movable pinion 90 is mounted on thecenter of the shaft 89 to mesh with the rack teeth 76 and 77 on the driving bar 1 and the rod 8. Theshaft 89 may be provided with a collar 91. The rack teeth 76 and 77 and the pinion 90 form the aforesaid differential gear means whereby the driving bar 1 and the rod 8 are simultaneously moved in the opposite directions relative each other. The return of this differential gear means to its illustrated initial position after operation, which is described hereinbelow, is automatically effected as the holder 26 with its sleeve 28 and shank 25 is pressed backwardly by the coil spring 22 positioned between the flange 32 and the cylinder 20.

In the above described embodiment of the invention shown in FIGS. 9 and 10, the driving bar 1 and so forth are free to move axially relative to the cylinder 20 and the holder 26. As this holder 26 is pressed forwardly,

urge the latter forwardly, and abutment means fixedly mounted on said driving bar for contact with the'outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing.

3. A back spotfacer according to claim 1, wherein said positive engagement means comprises pinion teeth formed'with said cutting arm and rack teeth formed with said rod in mesh with said pinion teeth on said cutting arm, the means for regulating the position of the cutting arm comprising a stop mounted within said driving bar and having a portion projecting forwardly out of said driving bar for contact with said cutting arm at a point adjacent the swingable end thereof and first the rod 8 coupled with the sleeve 28 by the pin 74 advances thereby turning the pinion 90 clockwise, as viewed in FIG. 9, with its rack teeth 77. The driving bar 1 is then moved backwardly relative to the rod 8 or the sleeve 28. When the rod 8 is advanced as aforesaid, the roller 4b of the cutting arm support 4a, which has been received in the transverse groove 83 on the rod 8, is now turned forwardly by the surface 84 and rides on the recessed surface 81. Hence, as indicated by the dotted lines in FIG. 9, the cutting arm 4 with its cutting bit 6 is turned to its operative position. As the rod 8 is further pressed forwardly, the driving bar 1 and therefore the cutting arm 4 are moved backwardly, thereby facing or counterboring a spot b to a desired depth.

Although the back spotfacer of the present invention has been shown and described hereinbefore in terms of several preferred embodiments thereof, the invention, itself, is not considered to be restricted by the exact showing of the drawings and the description thereof, but should be understood to include a latitude of modification, substitution and change. It is, therefore, appropriate that the appended claims be construed broadly and in a manner consistent with the fair meaning and the proper scope of the invention herein disclosed.

We claim:

1. A back spotfacer comprising, in combination:

a driving bar;.

,a cutting arm mounted on one end of said driving bar so as to be swingable between an inoperative position along the axis of said driving bar and an operative position in the radial direction of said driving bar;

adjustable means for regulating the position of the cutting arm and in contact therewith;

a rod extending through said driving bar so as to be axially slidable therethrough to turn said cutting arm between said inoperative and operative positions thereof;

positive engagement means for positive engagement between the cutting arm and the rod; and

a holder having a shank whereby the same is rotated with said driving bar;

said rod having moved axially of said driving bar by said holder.

2. A back spotfacer'according to claim 1, wherein said positive engagement means comprises pinion teeth formed with said cutting arm and rack teeth formed with said rod and in mesh with said pinion teeth on said cutting arm, said driving bar being free to move axially of said holder, and including spring means positioned between said holder and said driving bar to resiliently spring means for resiliently urging said stop forwardly, said driving bar being free to move axially of said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means fixedly mounted on said driving bar for contact with the outer surface of a work-piece when said driving bar is inserted into a hole therethrough for back spotfacing.

4. A back spotfacer according to claim 1, wherein said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, a stop mounted within said driving bar and having a portion projecting forwardly out of said driving bar for contact with said cutting arm at a point adjacent the swingable end thereof, first spring means for resiliently urging; said stop forwardly, means for adjusting the position of said stop, said driving bar and said rod being-free to independently move axially of said holder, said rod being moved forwardly relative to said driving bar by said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, third spring means for resiliently urging said rod backwardly relative to said driving bar, and abutment means fixedly mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for backspotfacing operation.

5. A back spotfacer according to claim 1, wherein said. cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, said holder being detachable, said driving bar and said rod being free to indepen dently move axiallyof said holder, said rod being moved forwardly relative to said driving bar by said holder, first spring means for resiliently urging said rod backwardly relative to said driving bar, a pin extending transversely through said holder and being received in a slot on the backward end of said rod to rotate the same with said holder, a resiliently yieldable projection extending from said driving bar into a groove formed axially on said holder, said groove having a curved bottom portion on which said resiliently yieldable projection is slidingly retractable to permit the detachment of said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation.

6. A back spotfacer according to claim 1, including abutment means mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for cording to the depth of said hole.

7. A back spotfacer according to claim 1, wherein said driving bar forms part of a front attachment, said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm; a sleeve interconnecting said holder and said front attachment for simultaneous rotation, said rod being moved forwardly relative to said driving bar by said holder; means for detachably securing said front attachment to said sleeve; first spring means for resiliently urging said rod backwardly relative to said driving bar; second spring means positioned between said holder and said sleeve to resiliently urge the latter forwardly; and abutment means mounted on said sleeve and said front attachment for contact with the outer surface of a workpiece when said front attachment is inserted into a hole therethrough for back spotfacing operation.

8. A back spotfacer according to claim '1, wherein said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, said driving bar being free to move axially of said holder, a safety pin mounted across a bore extending axially of said holder to support the backward end of said rod, said safety pin being collapsible upon application of a predetermined lateral pressure through said rod, spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation. 

1. A back spotfacer comprising, in combination: a driving bar; a cutting arm mounted on one end of said driving bar so as to be swingable between an inoperative position along the axis of said driving bar and an operative position in the radial direction of said driving bar; adjustable means for regulating the position of the cutting arm and in contact therewith; a rod extending through said driving bar so as to be axially slidable therethrough to turn said cutting arm between said inoperative and operative positions thereof; posiTive engagement means for positive engagement between the cutting arm and the rod; and a holder having a shank whereby the same is rotated with said driving bar; said rod having moved axially of said driving bar by said holder.
 2. A back spotfacer according to claim 1, wherein said positive engagement means comprises pinion teeth formed with said cutting arm and rack teeth formed with said rod and in mesh with said pinion teeth on said cutting arm, said driving bar being free to move axially of said holder, and including spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means fixedly mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing.
 3. A back spotfacer according to claim 1, wherein said positive engagement means comprises pinion teeth formed with said cutting arm and rack teeth formed with said rod in mesh with said pinion teeth on said cutting arm, the means for regulating the position of the cutting arm comprising a stop mounted within said driving bar and having a portion projecting forwardly out of said driving bar for contact with said cutting arm at a point adjacent the swingable end thereof and first spring means for resiliently urging said stop forwardly, said driving bar being free to move axially of said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means fixedly mounted on said driving bar for contact with the outer surface of a work-piece when said driving bar is inserted into a hole therethrough for back spotfacing.
 4. A back spotfacer according to claim 1, wherein said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, a stop mounted within said driving bar and having a portion projecting forwardly out of said driving bar for contact with said cutting arm at a point adjacent the swingable end thereof, first spring means for resiliently urging said stop forwardly, means for adjusting the position of said stop, said driving bar and said rod being free to independently move axially of said holder, said rod being moved forwardly relative to said driving bar by said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, third spring means for resiliently urging said rod backwardly relative to said driving bar, and abutment means fixedly mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation.
 5. A back spotfacer according to claim 1, wherein said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, said holder being detachable, said driving bar and said rod being free to independently move axially of said holder, said rod being moved forwardly relative to said driving bar by said holder, first spring means for resiliently urging said rod backwardly relative to said driving bar, a pin extending transversely through said holder and being received in a slot on the backward end of said rod to rotate the same with said holder, a resiliently yieldable projection extending from said driving bar into a groove formed axially on said holder, said groove having a curved bottom portion on which said resiliently yieldable projection is slidingly retractable to permit the detachment of said holder, second spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation.
 6. A back spotfacer according to claim 1, including abutment means mounTed on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation, said abutment means including a member screw-threadedly movable in the longitudinal direction of said driving bar whereby the axial length of said abutment means is adjustable according to the depth of said hole.
 7. A back spotfacer according to claim 1, wherein said driving bar forms part of a front attachment, said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm; a sleeve interconnecting said holder and said front attachment for simultaneous rotation, said rod being moved forwardly relative to said driving bar by said holder; means for detachably securing said front attachment to said sleeve; first spring means for resiliently urging said rod backwardly relative to said driving bar; second spring means positioned between said holder and said sleeve to resiliently urge the latter forwardly; and abutment means mounted on said sleeve and said front attachment for contact with the outer surface of a workpiece when said front attachment is inserted into a hole therethrough for back spotfacing operation.
 8. A back spotfacer according to claim 1, wherein said cutting arm is formed with pinion teeth, said rod being formed with rack teeth in mesh with said pinion teeth on said cutting arm, said driving bar being free to move axially of said holder, a safety pin mounted across a bore extending axially of said holder to support the backward end of said rod, said safety pin being collapsible upon application of a predetermined lateral pressure through said rod, spring means positioned between said holder and said driving bar to resiliently urge the latter forwardly, and abutment means mounted on said driving bar for contact with the outer surface of a workpiece when said driving bar is inserted into a hole therethrough for back spotfacing operation. 